So if I understand correctly, A Grand Cherokee will do it but not that good. A Pickup will do it pretty well but a trailer with brakes is best. Is that Right?
I'd recommend not flat towing
your Jeep with anything less than a full-size truck. I flat tow mine behind 3/4 ton Suburban, and it tows great. But I've talked to several people on RV.net who have towed their TJs with GCs and were very unhappy because the TJ pushed around the rear of the GC. A 3/4 Suburban is significantly heavier than a GC, and that helps a lot when you flat tow because the tow bar has no tongue weight.
A trailer is a completely different story. If you've got your trailer balanced correctly, you'll do pretty well with the GC.
With regards to brakes - you can add auxiliary brakes to any vehicle while in tow. There are several systems on the market, such as Brake Buddy, ReadyBrake by ReadyBrute, and Roadmaster EvenBrake. They can be pricey, but if you're going to flat tow the Jeep regularly, you'll be glad you have it. I've ocassionally flat-towed my LJ with my 3/4 ton Suburban without brakes, but I wouldn't recommend that with a 1/2 ton (lighter truck, smaller brakes, etc...).
If you're going to trailer tow the Jeep, then the trailer should have sufficient brakes (assuming it's rated to tow the Jeep's weight).
Also, a full-size SUV will do better flat towing than a full-size pickup because it'll have more weight on the read end, which will help offset the lack of tongue weight.
Hope that helps.